1. Field of the Invention
The present invention relates to a method for fabricating a semiconductor laser device, and more particularly to a method for fabricating a semiconductor laser device for providing high output.
2. Description of the Prior Art
FIGS. 1A to 1C are perspective views showing a method for fabricating a conventional semiconductor laser device in order of the manufacturing steps. The fabricating method of the conventional semiconductor laser device will be described. First, as shown in FIG. 1A, an N type GaAs layer 2 to be a current narrowing layer is deposited on a semiconductor substrate 1 of P type GaAs. Then, as shown in FIG. 1B, the GaAs layer 2 is selectively etched to form a striped groove 3 which is deep enough to reach the semiconductor substrate 1 and extends to that portion to be an end surface of a resonator. Then, a lower clad layer 4 of P type AlGaAs, an active layer 5 of P type AlGaAs, an upper clad layer 6 of N type AlGaAs and a contact layer 7 of N type GaAs are deposited in this order to form a semiconductor laser device shown in FIG. 1C.
The operation of a conventional semiconductor laser device will be described. Due to the presence of the current narrowing layer, the current over the active layer 5 does not flow over the entire surface but flows only along the portions adjacent to that region where the above described current narrowing layer breaks. The optical output rises as the current rises.
In a conventional semiconductor laser device fabricated according to the above described method, the active layer 5 extends uniformly to the end surface of the resonator, so that the energy band gap of the end surface becomes a little narrower than that of the central portion due to the nature of the molecule, resulting in the greater absorption of light than the emission of the light. Therefore, when the current is raised in order to increase the optical output, a breakdown occurs at the end surface because of the heat and the absorption of light.
A structure having no active layer at the end surface for preventing such breakdown is disclosed in, for example, H. Blauvelt, et al. "Large optical cavity AlGaAs buried heterostructure window lasers", Appl. Phys. Lett. 40(12), pp. 1029-1031, 15 June 1982, in which that portion to be the window at the end surface is made in such a manner that a cavity is formed at that portion by etching and then it is filled with AlGaAs of a new composition. This semiconductor laser device, however, still presents a problem that, although it lowers the density of light to preclude the deterioration, it is still subjected to deterioration due to the still occurring absorption of the light.